1. Technical Field
The present invention relates to an optical scanner, an image display device, a head mount display, and a heads-up display.
2. Related Art
An optical scanner for performing drawing by optical scanning has been used in a laser printer or an image display device. JP-A-2009-2978 discloses an optical scanner including torsion bars in two directions which are orthogonal to each other. By doing so, in the optical scanner, a movable plate is oscillatably supported by a pair of first torsion bars. A surface reflecting light is installed in the movable plate. The other end of the first torsion bar is connected to a frame-shaped displacement portion. In addition, the displacement portion is oscillatably supported by a second torsion bar. The other end of the second torsion bar is supported by a frame-shaped support portion. A direction in which the first torsion bar extends is set as a first direction, and a direction in which the second torsion bar extends is set as a second direction. The first direction and the second direction are orthogonal to each other. Accordingly, the movable plate can be oscillated by using the two directions orthogonal to each other as rotation axes.
In a plan view seen from a thickness direction of the movable plate, a unimorph driving unit is provided in the support portion with the second torsion bar interposed therebetween. The unimorph driving unit is a member for distorting and driving a piezoelectric element. The unimorph driving unit performs driving for twisting and driving for bending the second torsion bar. The movable plate and the displacement portion rotate by using the second direction as a rotation axis, when the second torsion bar is twisted. The movable plate rotates by using the first direction as a rotation axis, when the second torsion bar is bent. The unimorph driving unit is driven in a predetermined period. Accordingly, the movable plate and the displacement portion are oscillated by using the two directions orthogonal to each other as rotation axes.
The unimorph driving unit bends the second torsion bar by a horizontal scanning driving signal and twists the second torsion bar by a vertical scanning driving signal. The horizontal scanning driving signal has a frequency higher than that of the vertical scanning driving signal. The movable plate and the displacement portion are oscillated by the vertical scanning driving signal by using the second direction as a rotation axis. The movable plate is oscillated by the horizontal scanning driving signal by using the first direction as rotation axis.
JP-A-2005-250077 discloses an optical scanner including torsion bars in one direction. By doing so, in the optical scanner, a first movable plate is oscillatably supported by a pair of the torsion bars. One torsion bar portion is fixed to a support. The other torsion bar portion is connected to a second movable plate. A coil is installed on the second movable plate and a magnetic field acts on the coil, and accordingly the second movable plate is oscillated. The first movable plate oscillates by oscillation of the second movable plate. The second movable plate has a damper structure. A Q value of the optical scanner is decreased by the damper structure. This damper structure is not a mechanism for suppressing mutual effects of the two movable plates.
A miniaturized optical scanner is desirable in order to use the optical scanner in a portable device. When miniaturizing the optical scanner disclosed in JP-A-2009-2978, it is also necessary to miniaturize the displacement portion. When the displacement portion is miniaturized, an inertia moment of the displacement portion decreases. Accordingly, the displacement portion is easily affected by vibration with a high frequency. When the displacement portion oscillates by using the second direction as a rotation axis, the displacement portion is affected by the horizontal scanning driving signal, in addition to the vertical scanning driving signal. Since the movable plate oscillates by the oscillation of the displacement portion, the movable plate is affected by the horizontal scanning driving signal when being oscillated by using the second direction of the movable plate as a rotation axis. As a result, the movable plate is operated with an oscillation component which is unnecessary for the vertical scanning. Therefore, an optical scanner having an improved vibration performance so that the horizontal scanning hardly affects the vertical scanning even with the miniaturized optical scanner, has been desired.